1. Field of the Invention
This invention relates to rotor blades for turbomachines and, more particularly, to blades formed of high strength, high modulus fibers embedded in a matrix material.
2. Description of the Prior Art
The operational characteristics and desired attributes of rotor blading are well understood by scientists and engineers working in the turbomachinery field. Against this background very substantial research efforts continue to be applied to the development of material systems which will enhance the desired attributes of blades in their operational environment.
One desired characteristic is a high strength to weight ratio in the blade system. In recent years the extensive use of titanium has enabled dramatic increases in blade strength to weight ratios when compared to formerly used steel or aluminum blades. Titanium is now cnsidered to be the state of the art material for most compressor blade applications.
Another desired characteristic is a high stiffness to weight ratio. The high stiffness reduces the susceptibility of the rotor blades to deleterious effects of adverse vibratory stimuli. Substantial aerodynamic improvements are obtainable in blade systems having adequate torsional stiffness without part span shrouds.
Composite materials formed of high strength, high modulus fibers embedded in a matrix material have for the last decade held great promise for future dramatic increases in strength to weight and stiffness to weight ratios. Unfortunately, however, composite blades have, heretofore, had a notoriously low tolerance to foreign object damage. Developed systems, such as those shown in typical prior art U.S. Pat. Nos. 3,098,723 to Micks entitled "Novel Structural Composite Material"; 3,572,971 to Seiwert entitled "Lightweight Turbo-Machinery Blading"; 3,649,425 to Alexander entitled "Arcuate Shaped Composites of Refractory Tapes Embedded in a Metal Matrix"; 3,699,623 to Kreider entitled "Method for Fabricating Corrosion Resistant Composites"; and 3,762,835 to Carlson et al. entitled "Foreign Object Damage Protection for Compressor Blades and Other Structures and Related Methods", encase a brittle composite material in a more ductile, all metallic sheath to improve resistance of the composite structure to foreign object damage.
Further improvements enhancing the survivability of composite blades and enhancing the manufacturability of composite blades are required before full utility in turbomachines can be realized.